The present invention relates to the field of photography and, more particularly, to certain aspects of a camera including an automatic lens focusing system.
Commonly-assigned U.S. Pat. No. 4,167,316 and copending applications U.S. Ser. Nos. 17,196, now U.S. Pat. No. 4,243,309, and 17,425, now U.S. Pat. No. 4,315,676, both filed on Mar. 5, 1979, and U.S. Ser. No. 156,044, now U.S. Pat. No. 4,307,952, filed on June 3, 1980, disclose cameras of the type including an automatic lens focusing system that is formed in part by a sonic ranging system for measuring the photographic subject-to-camera distance. The focusing system is operated in a coordinated manner with the camera shutter blade mechanism.
Typically, the lens focusing system includes a plurality of discrete lens elements, each having a different focal length, mounted in circumferentially spaced apart relation on a lens holding disc for rotation about a center axis to sequentially present the lens elements at a focusing position for focusing image forming light rays emanating from a subject, located within a corresponding subject-to-camera distance range, at the camera's film plane.
As the sonic ranging system (which may be of the type described in commonly-assigned U.S. Pat. No. 4,199,246) operates, the disc is engaged by the arm of a torsion spring or the end of a pivoting actuator member to impart rotary motion thereto. After receipt of an echo signal from the subject indicative of subject distance, a disc pawl operates to engage a corresponding one of a plurality of notches or tabs disposed about the periphery of the disc to thereby stop disc motion and locate the lens element corresponding to the indicated distance range at the focusing position. Thereafter, the blade mechanism is operated to define the exposure interval.
In the above-noted copending application U.S. Ser. No. 156,044, the lens pawl is controlled electronically in response to receipt of the echo signal indication to insure that a notch engaging tang of the disc pawl first engages an outer edge of the disc between adjacent notches to prevent pawl bounce which may occur if the tang initially engages an edge of the notch thereby precluding its receipt therein to stop the disc. The electronically controlled timing of pawl release is correlated to the operating rotational velocity of the disc resulting from acceleration. Therefore, for this system to operate properly, the disc and its drive system must be configured for regulating the rotational velocity of the disc so that it consistently falls within a fairly narrow range of acceptable velocities.
The rotational velocity of the disc is, in turn, controlled by the acceleration force applied thereto to effect rotation. As set forth in more detail in commonly-assigned copending application U.S. Ser. No. 222,011 filed on even date herewith, the automatic lens focusing systems disclosed in the above-noted patent and copending applications derive acceleration energy from a remote source through complex mechanical linkages which tend to be rather expensive and difficult to calibrate accurately.
Therefore, it is an object of the present invention to provide in a camera having such an automatic lens focusing system simplified structure for more accurately rotatably driving the lens disc and means and methods for easily calibrating disc rotational velocity.
Other objects of the invention will, in part, be obvious and will, in part, appear hereinafter.